This invention relates to a method and structure for providing an air bypass to more quickly supply air during transition stages for gasoline direct injection engines.
Gasoline direct injection engines are known and have air supply flow line supplying air through an enlarged chamber, or plenum, under the control of a throttle valve. Air is delivered through the supply line to the engine piston cylinder, where it mixes with fuel. As known, during the control of this type engine, there are two distinct combustion modes. First, early injection occurs under stoichiometric operation, wherein the air to fuel ratio is relatively low. After initial startup, the air ratio increases dramatically. The air quantity required in late injection mode is typically at least double that of early injection mode.
The prior art operates well in adequately supplying air during both the early injection and late injection modes, once they have been achieved. However, there is actually a third mode, which is a transition mode between early injection and late injection. In this mode, the prior art has not always adequately delivered sufficient quantity of air to the engine as quickly as would be desired.
Applicant has determined the problem occurs due to the plenum in the path of the air injection line. Due to the relatively large plenum chamber volume, the increase in air flow to the plenum takes a period of time to be translated into an increase in air volume leaving the plenum and reaching the engine.
In a disclosed embodiment of this invention, an air bypass line is disposed to deliver a bypass quantity of air to the engine during the transition phase. This bypass quantity bypasses the plenum volume.
In a preferred embodiment of this invention the bypass line is relatively small compared to the main supply line. As an example, the bypass line could have a cross-sectional area which is less than half the cross-sectional area of the main supply line. In one preferred embodiment the quantity is actually less than a third of the area of the main supply line.
The valve is controlled by an ECU which also controls the engine. Thus, when the ECU begins to enter transition mode between early injection and late injection, the valve is open to allow the bypass air to reach the engine chambers. In this way, sufficient air is provided during this transition mode. Once the steady state operation has been achieved, the valve may again be closed although it may be left open to supplement the flow. This alternate control allows the plenum and main flow line to be smaller.
The preferred embodiment maintains the valve open at late injection to supplement the flow there through the main supply line. The method works when moving from late to early injection conditions and in a generally reverse manner. That is, beginning with late injection, the bypass valve is typically open. As the transition period is approached, this valve is closed, and remains closed at the early injection stage.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.